The crystalline lens is a transparent structure that focuses light in the human eye. Opacification of the lens known as cataract formation is a common cause of poor vision in the elderly, and can be corrected surgically.
Modern cataract surgery is performed by manual extracapsular cataract extraction, or by phacoemulsification. In both operations an opening is made in the anterior capsule to allow removal of the lens contents. The capsular bag remnant, however, is left in situ to provide support for an intraocular lens implant which is inserted following removal of the cataract to replace the focusing power of the natural crystalline lens.
It is known to provide an intraocular lens implant which typically comprises a central focusing element, known as an optic, and peripheral support structure, known as a haptic. The optic and the haptic of the intraocular lens may be manufactured from transparent rigid plastics material such as polymethyl methacrylate, or from flexible plastics material such as silicone or hydrogel. Intraocular lens implants manufactured from flexible material are preferable to those made of rigid material because the lens may be folded to allow insertion through a small incision in the sclera or outercoat of the eye and is then required to unfold to its original dimension.
The optic and haptic of the intraocular lens may be manufactured from the same material as a single piece unit or the haptic may be attached to the optic by a variety of mechanisms. There may be one or a plurality of haptics attached to the optic, although the most common configuration includes an optic with two outwardly extending haptics. The purpose of the haptic is to provide optimal centration of the optic as well as a means of fixation of the implant within a capsular bag remnant of the original lens following cataract or lens extraction. It is preferable that the haptics conform to the periphery of the capsular bag to provide a larger surface area of contact between the intraocular lens implant and the capsular bag and to ensure centration of the optic. It is also possible to implant a lens in front of the anterior capsule behind the iris with the haptics resting in the region between the root of the iris and cilairy processes, known as the cilairy sulcus. Intraocular lenses may also be inserted in phakic eyes to correct refractive errors, such as myopia or hyperopia, in front of the crystalline lens behind the iris with the haptic providing support in the cilairy sulcus. Furthermore, as an alternative site of implantation in phakic eyes, intraocular lenses may be inserted in front of the iris in the anterior chamber with the haptics resting in the angle of the anterior chamber.
A conventional intraocular lens 100 in accordance with the prior art shown in FIG. 1 comprises a central optic 101, and two haptics 102 connect with the central optic 101. As shown in FIG. 2, the conventional intraocular lens 100 is mounted in the capsular bag 200 of a human eye with the central optic 101 coaxially aligned with a vision axis A of the eye. However, an anterior chamber distance (ACD) is fixed (i.e., does not accommodate), the central optic 101 is not moveable along the vision axis A of the eye, and the refractive power of the lens cannot be adjusted. As shown in FIG. 3, the conventional intraocular lens 100 can also be mounted in the ciliary sulcus 300 of the human eye when the capsular bag 200 is not complete. The two haptics 102 of the conventional intraocular lens 100 are settled on the ciliary sulcus 300. However, the anterior chamber distance (ACD) is fixed, and the refractive power thereof cannot be adjusted.
Intraocular lenses differ with respect to their accommodation capability, and their placement in the eye. Accommodation is the ability of an intraocular lens to accommodate, which is to focus the eye for near and distant vision. Natural accommodation in a normal human eye involves shaping of the natural crystalline lens by automatic contraction and relaxation of the ciliary muscle of the eye by the brain to change the vitreous pressure of the eye and focus the eye at different distances. Ciliary muscle relaxation shapes the natural lens for distant vision. Ciliary muscle contraction shapes the natural lens for near vision.
Most non-accommodating implanted lenses have single focus optics which focus the eye at a certain fixed distance only and require the wearing of eye glasses to change the focus. Other non-accommodating lenses have bifocal optics which image both near and distant objects on the retina of the eye and provide both near vision and distant vision sight without eyeglasses. Bifocal intraocular lenses, however, suffer from the disadvantage that each bifocal image represents only about 40% of the available light and the remaining 20% of the light is lost in scatter.
What is still desired is a new and improved intraocular lens implant wherein the coaxial position of the central optic along the vision axis may be changed by control of the user and accommodate automatically. Preferably, the new and improved intraocular lens implant will utilize the ciliary muscle action and the vitreous pressure of the eye to effect accommodation movement of the lens optic along the vision axis of the eye between a distant vision position to a near vision position.